A typical gas spring for die stamping applications is constructed with an actuating rod connected to a piston slidably received in a cylinder having a cavity which is precharged to a predetermined pressure with an inert gas such as nitrogen. When the rod and piston are forced into the cavity the gas therein is compressed and when the force applied to the rod is removed, the compressed gas within the cavity immediately forces the piston and rod toward its fully extended position.
In some die stamping applications, gas springs adjacent a lower die half may be used to dislodge the stamped part from a cavity of a lower die half. A problem develops on the return stroke of the upper die half when typical gas springs are used because they immediately and rapidly return to their fully extended position and thereby quickly dislodge and lift the die stamped part from the lower die half. At least with parts having a somewhat large surface area, the rapid return of the gas springs toward their extended positions can cause the die stamped part to buckle or flex and thereby adversely affect the quality of the stamped part.
To delay or control the return of the piston and rod to their extended positions, some prior gas springs have utilized mechanical or electronic controls on the gas springs. Such controls are undesirable and increase the cost and complexity of the gas springs. Another type of gas spring, such as that disclosed in U.S. Pat. No. 5,823,513 uses hydraulic fluid in one chamber, compressed gas in another chamber and a delay valve to cause a momentary dwell at the bottom of the gas spring stroke. This dwell is provided to prevent damage to the press among other reasons. A critical aspect of any delay cylinder, is its ability to withstand and/or dissipate the heat generated in use.